Interpretive Summary: Moth caterpillars pose a food safety concern because aflatoxin- and other mycotoxin-producing fungi grow on agricultural crops especially when damaged by these pests. The use of synthetic sex pheromones (sex attractants) to control moth pests is an appealing alternative to the use of chemical pesticides. However, in order to fully exploit sex pheromones as caterpillar biocontrol agents, we need to understand how many genes are responsible for their production, whether or not all species possess the same genes, and how new or different pheromones are produced. In this study, we show that moth sex pheromone genes are highly diverse. We also found that species produce distinct pheromones by utilizing different genes. We propose that the differential gain and loss of these genes leads to the production of new and different pheromones.

Technical Abstract:
A great diversity of pheromone structures are used in the Lepidoptera for long-distance mating signals, although the signal/response channel appears to be narrow for each species. The conundrum is how signal divergence has occurred in the face of strong selection pressures against small changes in the signal. Observations of various closely related and morphologically similar species that use pheromone components biosynthesized by different enzymes and biosynthetic routes underscore the question as to how major jumps in the biosynthetic routes could have evolved with a mate recognition system that is based on responses to a specific blend of chemicals. Research on the desaturases used in the pheromone biosynthetic pathway for various moth species has revealed that one way to make a major shift in the pheromone blend is by activation of a different desaturase from mRNA that already exists in the pheromone gland. Data will be presented to support the hypothesis that this process was used in the evolution of the Asian corn borer (ACB) species. In that context, moth sex pheromone desaturase genes appear to be evolving under a birth-and-death process. According to this model of multigene family evolution, some genes are maintained in the genome for long periods of time while others become deleted or lose their functionality, and new genes are created through gene duplication. This mode of evolution appears to play a role in moth speciation, as exemplified by the case of the ACB and ECB species.